Is this printed on an inkjet printer & can you reprint that panel? If it were mine, I'd take out that section of quilting, remove the panel and hand sew the new one in place, then re-do the quilting. It would annoy the hell out of me to leave it, and your nephew most likely won't know the difference if you don't tell.
Or you could reprint the date on similar colored fabric and applique over, remove the old date if it shows thru the fabric.
I agree with Gay. These kinds of errors are difficult to correct in place, If you have another piece from the panel, reprint and re-quilt. I misspelled my granddaughter's name on a quilt (Anna vs Ana) and had to carefully pick out my attempt at cursive writing with a sewing machine without leaving holes in the fabric. It would have been easier to just replace the border with the correct spelling, but no I picked and picked and picked..